Determining the exact location of a mobile device (e.g., a mobile phone) in an environment can be quite challenging, especially when the mobile device is located in an urban environment among buildings, or is located within a particular building. Imprecise estimates of the mobile device's position can delay emergency personnel response times by sending emergency response personnel to the wrong area of a floor in a building, or even to the wrong floor of a building.
Since mobile devices operated by users are often mobile and the locations of the mobile devices vary over time, enhancements have been made to emergency response services to support users who dial emergency response numbers. In the United States (“US”), “Enhanced 911” (also referred to as “E911” or “e911”) services provide an estimate of a mobile device's position at a particular time. In some implementations of E911, one or more reference points (e.g., Wi-Fi access points, Bluetooth beacons, or other types of local area network transmitters) can be used to estimate the position of a mobile device that is within range of those reference point(s). “Reference points” may also be referred to in general as “beacons”. The estimated position can be a geodetic location, or a civic address which may optionally contain additional information such as apartment number, suite number, office/cubicle number and floor number. When a 911 call is placed from the mobile device, an estimate of the mobile device's position can be determined using trilateration or other known processes that compute an estimated position of a mobile device using locations of reference points in communication with the mobile device and measurements that estimate approximate distances between the mobile device and the reference point(s). The estimate of the mobile device's position can be returned to the Public Safety Access Point (“PSAP”) handling the 911 call with the mobile device.
In one approach for enhancing emergency response services to support mobile devices, the mobile device may scan for identifiers of reference points, such as Media Access Control (“MAC”) addresses (also known as the Basic Services Set Identifier for Wi-Fi access points) or Bluetooth Public Device Addresses (“BT-PDA”) for a Bluetooth reference point. Any identifiers of reference points that are detected by the mobile device may be used to look up locations of those reference points that are stored in a National Emergency Address Database (“NEAD”). The stored locations of the reference points, in addition to measurements made by the mobile device that estimate approximate distances between the mobile device and the reference points, may be used to estimate the position of the mobile device (e.g., using trilateration). The estimate of the mobile device's position can be returned to the PSAP handling the 911 call with the mobile device. Unfortunately, this approach cannot be used when locations of detected reference points are not stored in the NEAD.
An alternative to storing all reference point locations in the NEAD uses an external location server (ELS) for emergency response services supporting mobile devices. Instead of storing all reference point locations in the NEAD, the NEAD can store URLs or other source indicators that are indexed and identified using the identifiers of reference points detected by the mobile device. Such URLs or other source indicators may be used to identify particular entities (e.g., buildings, campuses, zones in an environment controlled by an enterprise or other entity). The NEAD can query a particular ELS using the URL or other source indicator, and provide that ELS with the detected identifiers of the reference points as well as an identifier of the mobile device (e.g., a MAC identifier of the mobile device). The ELS then sends a query to an External Location Controller (ELC) of an external entity based on the reference point identifier. The ELC can instruct the reference point and other reference points it controls to search for the identifier of the mobile device, and then compute an estimate of the mobile device's position using the locations of the reference points, in addition to measurements made by the reference points that estimate approximate distances between the mobile device and the reference points (e.g., using trilateration). The estimate of the mobile device's position (e.g., Geodetic location, civic location, or other) may then be returned to the PSAP through the NEAD.
Unfortunately, the above ELS-based approach cannot be used when the identifier of the mobile device is not available, or when the mobile device's identifier cannot be detected during the search by the reference points. Thus, solutions are needed to make locations of reference points available for computing an estimate of a mobile device's position when the NEAD does not store the locations of reference points and when the mobile device's identifier is either not available or cannot be detected by reference points.